Non-polarizing thin film edge filter and fiber optic communication systems incorporating such filters.

摘要

A thin film optical filter having a bandpass reflectance characteristic with one otthe transition wavelength edges thereof being non-polarizing for radiation incident at a preselected non-normalangle. The filter comprises a transparent substrate and a multilayer thin film optical coating provided on one surface thereof. The optical coating includes a preselected number of alternate layers of a first higher refractive index dielectric material and a second lower refractive index dielectric material arranged as a sequence of dielectric multilayer stacks with intervening spacer layers formed of one of the dielectric materials. The optical thickness of the spacer layers is detuned from half-wave optical thickness to shift either the low wavelength transition edges (Figure 10B) or the high wavelength transition edges (Figure 10A) for the separate bandpass response characteristics for the two principal polarization planes substantially into alignment with each other. Various other dielectric stack designs utilizing detuned layers to accomplish the same alignment of wavelength transition edges are described. Simplex and duplex fiber optic communication systems utilizing non-polarizing edge filters of the thin film type are also disclosed.